The present invention relates to integrated circuits which are protected from the environment. These circuits are inexpensive to fabricate and have improved performance and reliability.
Modern electronic circuits must be able to withstand a wide variety of environmental conditions such as moisture, ions, heat and abrasion. A significant amount of work has been reported directed toward various protective measures to minimize the exposure of such circuits to the above conditions and thereby increase their reliability and life.
Many prior art processes for protecting electronic circuits have involved sealing or encapsulating the circuits after they have been interconnected. For example, it is known in the art to use protective layers of silicones, polyimides, epoxies, other organics, plastics, and the like. Such materials, however, are of only limited value since most are permeable to environmental moisture and ions.
Similarly, interconnected circuits have also been sealed within ceramic packages. This process has proven to be relatively effective in increasing device reliability and is currently used in select applications. The added size, weight and cost involved in this method, however, inhibits widespread application in the electronic industry.
The use of lightweight ceramic protective coatings on electronic devices has also been suggested. For instance, Haluska et al. in U.S. Pat. Nos. 4,756,977 and 4,749,63 1 describe the use of ceramic silica coatings derived from hydrogen silsesquioxane and silicate esters, respectively, as well as additional ceramic layers as hermetic barriers. The present inventors have discovered that when such coatings are applied specifically to integrated circuits at the wafer stage and even though the bond pads are subsequently opened by removing a portion of the coating, the resultant circuits remain hermetically sealed and exhibit increased reliability and life.
Sealing circuits at the wafer stage is also known in the art. For example, it is known in the art to coat fabricated integrated circuits with ceramic materials such as silica and/or silicon nitride by CVD techniques. These coatings are then etched back at the bond pads for the application of leads. The wafers coated in this manner, however, have inadequate reliability and life.
The present inventors have now solved the above problems associated with the hermetic protection of integrated circuits by replacing the conventional passivation on integrated circuits with the silicon containing ceramic coating described herein.